Recent recognition of the health hazard associated with severe and mild hypertension has prompted clinicians to consider drug therapy even in cases involving only moderately elevated diastolic pressure. Consequently, an accurate determination of the diastolic pressure becomes increasingly important and desirable. A novel technique based on phase discrimination is described which would allow an unique determination of the true diastolic pressure without the delimma of choosing between Phase IV, Phase V and other haphazard criteria. When a Riva-Rocci cuff is inflated, a time lag generally exists between the arrival of the arterial upstroke and the generation of Korotkoff vibration. This time lag is at its maximum when the air pressure is at or near the systolic pressure, decreases steadily as the cuff pressure is lowered, and diminishes as the cuff pressure approaches the true diastolic pressure. The diminution of this time lag is easily detectable electronically and can be a more objective, reliable and accurate criterium for diastolic pressure indexing. This technique, based on time measurements, is also ideally suited for indirect diastolic pressure measurements in infants, shock patients, during cardiac stress testing and other situations where auscultation by human is most difficult and unreliable. A PHASE I program for preliminary verification of this new technique has been presented which includes large sample correlation studies involving conventional manual auscultation technique. PHASE II investigation constitutes correlation studies based on direct blood pressure measurements via indwelling catheter transducers in both primate and human subjects.